1. Field of the Invention
The present invention concerns a procedure to carry out test measurements on an X-ray computed tomography apparatus as well as a computed tomography apparatus.
2. Description of the Prior Art
Artificial test specimens are used on X-ray computed tomography (CT) to carry out test measurements and to calibrate or adjust the unit, particularly with respect to adjusting the size of the sampled area. Such test specimens are also called “phantoms”. Phantoms contain components of various specific densities in various geometric shapes. For example, a phantom of this type is described in German OS 198 52 324. Calibration of the CT apparatus is done with reference to cross-sectional views of such phantoms.
The required sampling and adjustments or calibration on a CT apparatus can be grouped in the following categories:                A. Adjustments made daily by the user as part of a regular routine.        B. Test measurements made by the user as part of a regular routine, perhaps monthly, to test the quality of the measurement results.        C. Adjustments made by repair personnel after exchanging hardware components, for example.        D. Adjustments made during construction of the CT.        
The adjustments listed above may be related in part, i.e. an adjustment in category C may require a subsequent adjustment in category A.
Most of the specified adjustments and test measurements require that one, and in most instances more than one phantom, be inserted in the CT apparatus in a precise Z-position (the z-axis being parallel to the system axis around which rotation occurs). It may also be necessary to specify certain parameters for each phantom prior to measurement. This procedure is time consuming and requires subject matter knowledge.
A simplification of the procedure has been proposed in a CT apparatus that sends program-controlled prompts to the user. The user instructions lead the service personnel through a pre-determined series of steps to mount the phantom correctly and in the proper Z-position, as well as to enter the parameters required for calibration. The proposed user instructions generally assure that all steps are appropriately made in the correct order. Nonetheless, this procedure is also time consuming.
A further proposal to simplify the procedure replaces the need (if it exists) to use multiple phantom bodies, with a combined phantom. This reduces the time required to exchange and calibrate the various individual phantoms. Nonetheless, the use of a combined phantom still requires mounting it in the CT apparatus in the proper Z-position. Calibration requires the entry of the parameters for the combined phantom in the proper sequence. That is also time consuming and requires subject matter knowledge to some degree.